It has been customary in the past to carry out an electrolysis procedure in which the desired product (s) are produced at one electrode (commonly referred to as the working electrode) while at the other (or counter) electrode a sacrificial reaction is carried out. For example, in the commercially practiced electrohydrodimerization (EHD) of an activated olefin such as acrylonitrile to adiponitrile, as in Equation 1 infra, wherein the useful product is produced at the cathode, the counter reaction (at the anode) is the sacrificial oxidation of water. EQU 2H.sub.2 C.dbd.CHR.fwdarw.R(CH.sub.2).sub.4 R (Equation 1)
where R=--CN,--CO.sub.2 Me,--CO.sub.2 Et, etc.
This reaction results in only 50% of the total electric power supplied to the cell being utilized for producing a useful synthetic product.
The efficiency (power utilization) of electrochemical processes could be greatly enhanced if the sacrificial reaction occurring at the counter electrode could be replaced with a useful reaction at such electrode where a useful product would be produced. An example of such a useful reaction in combination with that of Equation 1 would be an anodic Kolbe or Crum-Brown-Walker (CBW) reaction in which, for example, a monoester adipate undergoes decarboxylative dimerization to form a diester sebacate as in Equation 2 which follows: ##EQU1## where R'=alkyl.
Normally, when the CBW reaction is carried out in an electrolysis cell, the sacrificial reaction that is carried out at the cathode is the conversion of water to hydrogen and hydroxide when water is the electrolyte medium or the conversion of methanol to hydrogen and methoxide when methanol is the electrolyte medium.
The EHD reaction of activated olefin, as above, in the normal electrochemical mode, where the oxidation of water is used as the sacrificial anodic reaction, is carried out in aqueous solution at a pH of about 8-10 and requires the use of an electrolyte containing R.sub.4 N.sup.+ moieties. Such reaction usually gives hydrodimerized olefin yields of about 90% with current efficiencies of about 80-85%.
On the other hand, the CBW reaction is generally carried out in methanol (water can be used but the current efficiency is only about 35%) using a platinum or vitreous carbon anode together with an alkali metal or R'.sub.4 N.sup.+ cation and at a pH of about 3 to 4. Using these conditions the yield of dimer is about 90% and the current efficiency is about 65%. Generally the presence of anions other than the carboxylate in the CBW reaction will suppress the formation of the desired radical intermediate.
Attempts to carry out the above electrolytic reactions simultaneously in an undivided cell using aqueous acetonitrile as the electrolyte resulted in the producition of at least 23 different products in approximately equal amounts. Moreover, attempts to convert acrylate to adipate at the cathode and a monoalkyl adipate to a dialkyl sebacate at the anode of an undivided cell results in the trapping of intermediate CBW radicals (e.g., MeO.sub.2 C(CH.sub.2).sub.4 CH.sub.2.sup..) by activated olefin (acrylate) to give unwanted radical addition products.
In so far as we are aware, the only electrolytic systems capable of functioning to produce simultaneously products of the kind referred to above at both the anode and cathode, while substantially avoiding the formation of undesirable by-products, has been by the use of an electrolytic cell containing a selective permeable membrane or diaphragm which separates the anolyte from the catholyte and thus prevents the anolyte from contacting the cathode and the catholyte from contacting the anode. While satisfactory electrolytic reactions can be achieved by such an arrangement, the resultant apparatus is not as efficient as desired because the membrane increases the voltage loss, therefore decreasing the power utilization, and thus reducing the product production per unit of power utilized. Also additional equipment is required to be used with the cell to control the electrolytic process. In addition, the special membranes required in such a process add to the cost of the equipment and impose an economic penalty on the practice of the process.
There are also known processes in which events occurring at both electrodes are involved in production of a particular product, e.g. propylene oxide is prepared from propylene in an electrolysis involving oxidation of halide to halogen at the anode and reduction of water to obtain hydroxyl ion at the cathode, with both the halogen and hydroxyl being involved in epoxidation of the olefin. However, in such processes there is generally no provision for keeping materials separated since both anodic and cathodic products must contact the organic reactant material. Moreover, a single useful product is produced, rather than useful products at both electrodes.
U.S. Pat. No. 4,191,619 to Bernd D. Struck issued Mar. 4, 1980 proposes the use of an electrolytic cell which accomplishes some of the benefits of the prior art membrane partitioned cells by substituting cheaper materials for separating the anolyte and catholyte fluids, but nevertheless requires the use of an electrolytic cell which is more complicated and expensive than is desired, and this translates into a process which is burdened with a higher capital and maintenance cost.
The present invention, therefore, has the object of providing simple electrolytic cells which enable the practice of processes such as referred to above, in which useful products are produced at both electrodes without the use of special costly permeable membranes, permeable diaphragms and/or partitions thereby effecting a saving in cell cost and operation. Another object of this invention is to provide electrolytic processes utilizing such simple electrolytic cells.